1. Field of the Invention
This invention relates to electronic circuit simulation, and more particularly to analog circuit simulators.
2. Description of the Prior Art
The design of analog circuitry has always been a challenging task in view of the interaction between circuit components. The operation of circuit components depends quite strongly upon the range of values of control variables applied to the device. For example, depending upon the manner in which a bipolar junction transistor (BJT) is biased, the BJT will operate in a saturated mode or a non-saturated mode. Even in the non-saturated mode, the BJT performance varies quite significantly. Variations in BJT performance will, in turn, affect the manner in which biasing components interact with the BJT, also altering the performance of the BJT.
The simplicity of interconnecting a circuit during the design phase and energizing it while its performance is monitored has a strong appeal. However, the simplicity is deceiving. Should the performance of the circuit not meet expectations, it is often difficult to reliably predict how a circuit should be modified so that the desired performance will be achieved. Furthermore, by simply energizing a circuit, an operator runs the risk of exceeding current and/or voltage tolerances for the components of the circuit, creating the potential that components will be destroyed.
To help circuit designers predict more reliably the performance of circuits they are designing, circuit simulators have been created. Such simulators typically employ equations to represent operating characteristics of components. A well known example is the circuit simulation program SPICE. SPICE operates by employing equations which attempt to mathematically define the operation of circuit components. A fundamental problem with the use of equations to represent components is that typically, the operation of components cannot be defined by simple equations. Many circuit components operate through the interaction of a number of physical principles which all must be taken into consideration when mathematically describing the operation of a component. This creates a trade-off which must be resolved. To achieve a high degree of accuracy, complex equations must be employed which are difficult to work with. However, simplified equations produce inaccurate results.
Examples of known circuit simulators are described in the following U.S. Pat. No.: 4,527,249 which describes a logic circuit simulator, U.S. Pat. No. 4,215,420 which describes a parity simulator, U.S. Pat. No. 3,702,003 which describes an algorithm to minimize iterative computation of a system such as electronic circuits and U.S. Pat. No. 4,293,916 which describes apparatus for simulating thermocouples to calibrate or adjust apparatus which employs the output from thermocouples. The '916 patent does suggest that characteristic curves of the thermocouples may be stored and employed to simulate the output of the thermal couples. However, nowhere in this patent is there any suggestion of how an analog circuit simulation might advantageously employ characteristic curves to accurately analyze the operation of the circuit.